Australian Patent 495,414 describes apparatus for purification of water by continuous vacuum distillation. Distillation separates water from dissolved solids, for example salts, and from higher boiling point substances which are concentrated in the still residue. However, in a continuous distillation process, a substance of lower boiling point than water which is present in the feed may be vaporised in the still and condensed along with the water distillate. A number of insecticides and other organic pollutants now frequently occur in water obtained from natural sources and such low boiling contaminants may not be satisfactorily removed during conventional continuous distillation.
Conventionally low boiling contaminants are removed by subjecting water to batch distillation in a still. The contaminants boiling at a lower temperature than water are first removed as volatiles. Temperature is then increased to vaporise water. The first water fraction obtained is used to purge the condensor system and must be rejected, subsequent water fractions being retained.
Batch distillation methods are relatively expensive to conduct in comparison with continuous distillation. An object of the present invention is an improved method for continuous distillation which enables removal of low boiling volatiles from a higher boiling distillate and which is more efficient than batch distillation systems. Preferred embodiments of the invention are of relatively low capital cost and/or operating cost and operate at high efficiency.